Re: [PATCH V1] mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction

Re: [PATCH V1] mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction

[Jon Hunter]

On 28/11/2025 11:37, Harry Yoo wrote:
> Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab
> caches when a cache is destroyed. This is unnecessary when destroying
> a slab cache; only the RCU sheaves belonging to the cache being destroyed
> need to be flushed.
> 
> As suggested by Vlastimil Babka, introduce a weaker form of
> kvfree_rcu_barrier() that operates on a specific slab cache and call it
> on cache destruction.
> 
> The performance benefit is evaluated on a 12 core 24 threads AMD Ryzen
> 5900X machine (1 socket), by loading slub_kunit module.
> 
> Before:
>    Total calls: 19
>    Average latency (us): 8529
>    Total time (us): 162069
> 
> After:
>    Total calls: 19
>    Average latency (us): 3804
>    Total time (us): 72287
> 
> Link: https://lore.kernel.org/linux-mm/0406562e-2066-4cf8-9902-b2b0616dd742@kernel.org
> Link: https://lore.kernel.org/linux-mm/e988eff6-1287-425e-a06c-805af5bbf262@nvidia.com
> Link: https://lore.kernel.org/linux-mm/1bda09da-93be-4737-aef0-d47f8c5c9301@suse.cz
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
> ---

Thanks for the rapid fix. I have been testing this and can confirm that 
this does fix the performance regression I was seeing.

BTW shouldn't we add a 'Fixes:' tag above? I would like to ensure that 
this gets picked up for v6.18 stable.

Otherwise ...

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Thanks!
Jon

-- 
nvpublic

Re: [PATCH V1] mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction

[Harry Yoo]

On Tue, Dec 02, 2025 at 09:29:17AM +0000, Jon Hunter wrote:
> 
> On 28/11/2025 11:37, Harry Yoo wrote:
> > Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab
> > caches when a cache is destroyed. This is unnecessary when destroying
> > a slab cache; only the RCU sheaves belonging to the cache being destroyed
> > need to be flushed.
> > 
> > As suggested by Vlastimil Babka, introduce a weaker form of
> > kvfree_rcu_barrier() that operates on a specific slab cache and call it
> > on cache destruction.
> > 
> > The performance benefit is evaluated on a 12 core 24 threads AMD Ryzen
> > 5900X machine (1 socket), by loading slub_kunit module.
> > 
> > Before:
> >    Total calls: 19
> >    Average latency (us): 8529
> >    Total time (us): 162069
> > 
> > After:
> >    Total calls: 19
> >    Average latency (us): 3804
> >    Total time (us): 72287
> > 
> > Link: https://lore.kernel.org/linux-mm/0406562e-2066-4cf8-9902-b2b0616dd742@kernel.org
> > Link: https://lore.kernel.org/linux-mm/e988eff6-1287-425e-a06c-805af5bbf262@nvidia.com
> > Link: https://lore.kernel.org/linux-mm/1bda09da-93be-4737-aef0-d47f8c5c9301@suse.cz
> > Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> > Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
> > ---
> 
> Thanks for the rapid fix. I have been testing this and can confirm that this
> does fix the performance regression I was seeing.

Great!

> BTW shouldn't we add a 'Fixes:' tag above? I would like to ensure that this
> gets picked up for v6.18 stable.

Good point, I added Cc: stable and Fixes: tags.
(and your and Daniel's Reported-and-tested-by: tags)

> Otherwise ...
> 
> Tested-by: Jon Hunter <jonathanh@nvidia.com>

Thank you Jon and Daniel a lot for reporting regression and testing the fix!

-- 
Cheers,
Harry / Hyeonggon